In competitive or recreational weightlifting, weights are often dropped from a height and allowed to fall unguided until they strike the floor. For example, in Olympic weightlifting events such as the Snatch and the Clean and Jerk, a weightlifting bar with attached weight plates is dropped from above the athlete's head directly onto the floor surface or lifting platform at the level of the athlete's feet. In non-competitive weightlifting, it is also common for the weightlifter to drop his weights, particularly when performing certain exercises, such as deadlifts, bench presses, and overhead presses. When lifting heavy or maximum weight, a weightlifter may be unable to control the drop and may risk injury to himself if he does so. Alternatively, if the weightlifter were to stay in control to the extent that he could guide the weight to the floor after his lift rather than dropping it, he would not be able to lift his maximum weight.
This unguided drop of a heavy weight can result in damage to the equipment itself, the floor, and any nearby objects. In addition, the freely dropped weight risks injury to persons standing near it, such as the weightlifter who dropped it.
International Weightlifting Federation (IWF) Technical Rules, which are used in the Olympic Games and World Weightlifting Championships, require that any plates used in competition be covered in rubber or plastic. Non-competition weight plates are also often rubber-coated or fully rubber to reduce damage to the weights and the weightlifting floor. Such plates are often called bumper plates, Olympic plates, or elite plates. These rubber or rubberized plates rebound even higher than non-rubber plates upon hitting the floor, and the weights may collide with the weightlifter's shins, knees, or other body parts and cause an injury.
To minimize this risk of injury due to the rebound, some bumper weights seek to minimize bounce based on the type of rubber they utilize. But such lower bounce rubber weights can bring about other problems, such as being too wide to meet competition standards, being limited in the maximum mass, or suffering cracking over time.
Another important concern in the sport of competitive weightlifting is the accuracy of the weights used. For example, IWF rules require tight tolerances for the weights used: +0.1% and −0.05% per weight weighing more than 5 kg and +10 grams and −0 grams per part weighing less than 5 kg.
Manufacturing solid weights in a single piece can present difficulties in meeting these tight tolerances required for competitive weightlifting under IWF rules. For example, typical tolerances expected in steel castings under 45 kg are approximately ±5%. See Steel Castings Handbook 16-13 (Malcolm Blair and Thomas L. Stevens, 6th ed. 1995). Many labor intensive operations may be employed to control cast weights to tight tolerances, including grinding, milling, or filing. In the field of weightlifting, solutions to meeting tight tolerances have included designating a specific area of the weight to be filed or milled to decrease the weight. See, e.g., U.S. Pat. No. 7,517,305, Col. 6:11-14. Another solution to manufacturing weights to meet tight tolerances include adding indentations to a weight where additional material may be added after casting and kept in place by way of packing, resin, or a covering. Id., Col. 6:15-35. In all events, the difficulty in meeting these tight tolerances adds significantly to the cost of the weight to the end-consumer.